As shown in FIG. 1, the RC-IGCT 100 includes within one wafer 10 an integrated gate commutated thyristor (IGCT) part 9 with IGCT cells 91 and a single built-in free-wheeling diode 97.
FIG. 2 shows a cut through an RC-IGCT according to a known implementation. The reverse-conducting semiconductor device 100 also includes a wafer 10 with layers of different conductivity types between a first main side 11, which is the cathode side of the integrated IGCT, and a second main side 15, which is the collector side of the IGCT cells 91 and which lies opposite the emitter side 11 (FIG. 2). The device includes IGCT cells 91, each of which with the following layers from the first main side 11 to the second main side 15: a cathode electrode 2 in form of a cathode metallization layer, a first (n+)-doped cathode layer 4, a (p)-doped base layer 6, an (n−)-doped drift layer 3, an (n)-doped buffer layer 8, a (p+)-doped first anode layer 5 and a first anode electrode 25 in form of an anode metallization layer. The plurality of IGCT cells 91 form the IGCT part 9 of the reverse conducting semiconductor device 100.
The IGCT cells 91 include a gate electrode 7, by which they are controlled. It is arranged as a gate metallization layer on the first main side 11. The gate electrode 7 is arranged lateral to, but separated from the cathode electrode 2 and the first cathode layer 4 and contacts the p-doped base layer 6. In the context of the present disclosure, “lateral” in describing layers means that two layers are arranged lateral to each other in view of a plane parallel to the first main side 11.
For reverse-conducting semiconductor devices 100 as shown in FIG. 1 a single freewheeling diode 97 is integrated on the same wafer 10. This single diode 97 is arranged lateral to the IGCT part 9 and includes on the first main side 11 a second (p)-doped anode layer 55 and in orthogonal projection to the area of the second anode layer 55 a second (n+)-doped cathode layer 45 on the second main side 15.
A plurality of the IGCT cells 91 can be arranged as stripes radially on a circular wafer 10. Stripes shall be understood as layers, which have in one direction a longer extension than in the other directions by having two longer sides, which can be arranged parallel to each other. Between the radially arranged IGCT cells 91 are the gate electrodes 7 arranged. The diode can be arranged as a single diode 97 either in the central part of the circular wafer or at the circumference of the wafer. If the single diode 97 is arranged in the central part, the IGCT part 9 is arranged on the circumference, the single diode 97 and IGCT part 9 being separated by a gate contact 75, to which the gate electrodes 7 are in electrical contact. For the single diode 97 being arranged at the circumference of the wafer 10, the IGCT part 9 is arranged in the central part and separated from the single diode 97 by the gate contact 75 or the IGCT part 9 is arranged adjacent to the diode 97 and the gate contact 75 is arranged in the central part.
In any case, the single diode 97 can be completely separated from the IGCT part 9 with no interaction between each other. That means if heat is created during operation of the device the heat is either generated in the single diode 97, if the device works in diode mode, or in the IGCT part 9, if the device is operated in IGCT mode. This might lead to overheating problems. Additionally, as the single diode 97 and IGCT part 9 are either strictly dedicated for diode or IGCT mode, this results in a large device.
EP 0 676 812 A describes a MOS controlled thyristor (MCT). Such devices can be operated only at much lower switching frequencies than GCTs and also the switched power is much lower. Such MCTs have an insulated gate and one common continuous p layer, which functions as anode layer for the diode cells as well as base layer in the MCT cells. A plurality of thyristor cells (forming a pilot MCT cell) is separated from another such plurality of thyristor cells by diode cells, which surround each set. The diode cells are of a sufficient width that no carriers can flow through a diode cell. If a set of thyristor cells is inoperable due to defects, these cells are not activated, so that the device can still be operated.
However, the MCT is turned off with a voltage pulse (MOS channel control) and not with a current pulse as for the GCT. Also the current is drawn out during turn-off from the gate in the GCT, whereas for the MCT it is forced to turn-off while the current drops through the main cathode by providing a MOS path. Hence for an MCT it can be easy to provide a diode area since its introduction is not affected by the gate control. As a result, such MCT devices face different technical specifications and are used for different applications than GCT devices.